For one Mexico has it's own part of the Americas ---also when the previous immigrants came, there was lots of empty land to homestead. Now there isn't and we already have cities that are plenty big enough. Where do you intend to put all the Mexicans you want to bring here? Should they be forced to build new towns --(except there is no vacant land left) or make our already big cities much bigger? Mexico City is huge ---if we bring everyone from there here ---that's a city far bigger than NY ---so where do they all go?
Most of us do not care to see this country turned into one, which is what you are trying to promote.
Yes we are a wealthy country, and I for one would like to see it stay that way. What you suggest is not the way to go about it.
Not to mention the security risks.
Have a nice entitled life, comrade.